textproduct: Albany

WHAT HAS CHANGED

While there remains uncertainty in the exact placement of the heavy rainfall axis for Sunday night into Monday, the latest probabilistic and ensemble guidance indicates only a very low chance for exceeding 2 inches in 24 hours across eastern NY and western New England. However, given recent heavy/locally extreme rainfall this pas week, be prepared for potential isolated to scattered flash flooding impacts in eastern and western New England.

There is now a marginal risk (level 1 of 5) for severe weather on Monday focused in the mid-Hudson Valley into western New England.

KEY MESSAGES

1) There is a medium to high chance for widespread rain and thunderstorms across eastern NY and western New England tomorrow afternoon through Monday resulting in isolated to scattered instances of flash flooding. Areas most at risk for flash flooding will be those that received high rainfall amounts this past week.

DISCUSSION

KEY MESSAGE 1...

After some isolated diurnally driven showers and thunderstorms this afternoon, ridging becomes established over the western Atlantic downstream of a split flow pattern. While a broad northern branch trough tracks through southern Canada, a cut- off low in the southern branch slowly tracks through the Midwest. As was discussed in the previous discussion, there remains discrepancies on whether these two features phase or not tomorrow into tomorrow night which will determine where the heavy rainfall axis sets-up. Latest trends still indicate the northern branch will help focus and direct the initial moisture axis and forcing for ascent around the Saint Lawrence River Valley tomorrow, supporting periods of rain and thunderstorms. While the most widespread rain/storms looks to occur mainly west of eastern NY, a few weak embedded shortwaves tracking within the strengthening south to southwesterly flow over the Northeast will likely support scattered showers and thunderstorms. As the northern and southern branch features interact, a nearly full latitude trough develops upstream, allowing the wind regime to tap into the Gulf and advect a very moisture rich air mass into the Northeast. In fact, PWATs increase towards 2" or within the 99th percentile of the NAEFS model climatology for this time of year. Thus, any isolated to scattered thunderstorms that develop will be capable of producing heavy downpours. With 20-30kts of deep layer shear, cannot completely rule out brief damaging winds from any storm that can grow upscale; however, ample cloud coverage in a highly moist environment should keep lapse rates weak and thus limit instability, keeping any severe storms isolated. We are not currently outlook in SPC's Day 2 Convective Outlook but remain in general thunder.

Heading into Sunday night, the northern branch in southern Canada looks to slow down and strengthen, even taking on a negative tilt while the once cut-off low escapes into the TN Valley and weakens as it becomes sheared out. Latest guidance shows a jet streak over the Northeast developing Sunday night with the continued unidirectional southerly winds over the Northeast maintaining a rich supply of warm air and moisture advection. Showers and embedded convection expand eastward Sunday night into eastern NY and western New England ahead of the approaching parent trough; however, there is increasing consensus in a secondary sfc low developing in the favorable equatorward entrance region of the jet streak. Where this feature develops will be key as it looks to focus the moisture/forcing leading to a heavy rain axis late Sunday night into Monday morning. There remains discrepancies on where this axis develops with one cluster favoring the mid-Hudson Valley, NW CT into New England while a second cluster shows it further northwest into more of eastern NY.

Given the recent heavy/locally extreme rainfall much of eastern NY experienced this past week, most soils are saturated and rivers/streams are elevated. 1hr and 3hr flash flood guidance values remain low ranging from 1 to 2.5 inches so if these values are exceeded, flash flooding concerns will increase. Given the anticipated highly moisture rich environment with forecast soundings showing high freezing heights 12-13kft and tall/skinny CAPE, efficient warm rain processes will be at play likely supporting high rainfall rates, especially within the heavy rain axis. However, unlike the recent heavy rain event, this seems to be a more progressive pattern as the trough continues to swing eastward into Monday. Thus, even if heavy rain can persist over a given area, it does not look to last multiple hours which lowers the potential for widespread flooding concerns. In addition, latest probabilistic guidance shows just a few isolated spots with very low values for 24hr rain amounts between 8PM Sunday and 8PM Monday exceeding 2 inches with even the 90th percentile for most of eastern NY and western New England under 2 inches in 24hrs. Therefore, WPC maintained its marginal to slight risk for excessive rainfall in the Day 3 Outlook (12 UTC Mon to 12 UTC Tues) messaging isolated to scattered flash flooding. The slight risk is focused in the eastern Catskills, mid-Hudson Valley and NW CT where the heavy rain axis looks to set-up late Sunday night into Monday but given continued discrepancies on the exact placement, this could change in future updates. Regardless of the slight risk location, it is important to be prepared for the potential for isolated to scattered flash flooding Sunday night into Monday in eastern NY and western New England. Areas that were hard hit with heavy rain this past week will be most vulnerable to renewed flooding concerns.

SPC also introduced a marginal risk for severe weather in the Day 3 Outlook for Monday focused mainly south and east of the Capital District given the potential for storms to grow upscale as the trough axis pushes through in the afternoon within the highly moist environment and 30-35kts of deep layer shear. Damaging winds is the primary hazard from any severe storm.

AVIATION /07Z SATURDAY THROUGH WEDNESDAY/

Through 06Z Sunday... Calm winds and mostly clear skies will allow radiational mist/fog to form across all terminals throughout this overnight period. KGFL starts off this period with LIFR vis, while KALB, KPOU, and KPSF are expected to lower to IFR/LIFR through 12Z. The greatest vis restrictions are expected at KGFL and KPSF, while KPOU will transition to prevailing LIFR and KALB sees only temporary IFR vis/cigs through 11Z.

This mist/fog will burn off by late Saturday morning, returning all terminals to VFR conditions by 14Z. High clouds will gradually fill in and lower throughout the afternoon and evening, with a few fair weather cumulus expected to develop throughout the same time period. Calm to light and variable winds will transition to southerly winds by the afternoon, persisting through the end of the TAF period.

Outlook...

Sunday Night: High Operational Impact. Likely SHRA...TSRA. Monday: High Operational Impact. Definite SHRA...TSRA. Monday Night: Low Operational Impact. Slight Chance of SHRA...TSRA. Tuesday: Low Operational Impact. Slight Chance of SHRA...TSRA. Tuesday Night: Low Operational Impact. Slight Chance of SHRA...TSRA. Wednesday: Moderate Operational Impact. Chance of SHRA...TSRA. Wednesday Night: Moderate Operational Impact. Chance of SHRA...TSRA. Thursday: High Operational Impact. Likely SHRA...TSRA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.